LDCT Scans Gain Support Amid Lingering Concerns

Heather Wakelee, MD

Assistant Professor, Oncology Member, Stanford Cancer Institute Stanford University School of Medicine Stanford, CA

Three medical societies have joined in endorsing low-dose computed tomography (LDCT) screening for patients at high risk of developing lung cancer, but with cautionary comments about unanswered questions over the potential harms of the scans and the difficulty of implementing the guidelines in clinical practice.

In May, the American Society of Clinical Oncology and the American College of Chest Physicians issued joint guidelines focusing on older patients with a history of heavy smoking after a systematic review of available research. The American Thoracic Society also endorsed the findings.^1,2

The recommendations call for annual LDCT screening of people aged 55 to 74 who have smoked for ≥30 pack-years and either continue to smoke or have quit within the past 15 years. Screening is not recommended for smokers who have smoked <30 packyears, are younger than 55 or older than 74, have quit smoking >15 years ago, or have severe comorbidities.

In addition, the guidelines recommend that screenings be conducted in locations that can offer the same comprehensive care and expertise with LDCT as sites that participated in the National Lung Screening Trial (NLST), which involved 53,454 current or former smokers from 33 sites across the country.

The trial found that screening with LDCT reduced the number of lung cancer-related deaths (Table).

Table. NLST Data

on Lung Cancer Mortality²

Number of events per screening method (%)

LDCT

356 (1.3)

Control

443 (1.7)

Rate of events per 100,000 person-years

LDCT

247

Control

309

Relative risk (95% CI) with LDCT

0.80 (0.73-0.93)

Number needed to screen to prevent 1 event

320

^*LDCT indicates low-dose computed tomography;

NLST, National Lung Screening Trial.

Heather Wakelee, MD, who specializes in thoracic malignancy research, believes the NLST results are noteworthy but shares concerns over implementing screening programs.

“Before the results of this study were made available, we didn’t have solid data,” said Wakelee. “This study was really the first to show a clear mortality benefit.”

An estimated 8 million Americans would fall under the recommended screening criteria and as many as 4000 lives could be saved annually, leading researchers have said. However, Wakelee said that while the benefits are clear for this particular population, there are a number of concerns that remain.

For example, Wakelee said that the risk of developing secondary malignancies as a result of the radiation is unknown because there has not been enough follow-up of patients in the NLST to determine that risk. Patients were followed for five years. Without knowing that risk, Wakelee said it could be difficult making similar recommendations to at-risk patients in a younger age range.

Additionally, the rate of false-positives found with LDCT lung cancer screening is significantly higher than with chest x-rays. Wakelee said that studies have shown that the rate of false-positives with LDCT is approximately 25%, while the rate of false-positives found with chest x-rays is closer to 7%.

“We have to determine what algorithm is needed with these different nodules,” Wakelee said. “It might mean following up with another scan in three months instead of a year.”

Wakelee also said that the low-dose form of LDCT used in the NLST is not typically what pulmonologists and oncologists use for screening. Additionally, there is no standardized measure of what a pulmonologist would use to determine how large a mass needed to be in order to suggest it was potentially cancerous.

Wakelee suggested that clinics approach screening with a team-based mentality by keeping open communication between pulmonologists and oncologists to better interpret any information acquired through LDCT screening.

References

1. Statement from the American Society of Clinical Oncology and the American College of Chest Physicians on the joint systematic review and clinical practice guideline on the role of CT screening for lung cancer (endorsed by the American Thoracic Society). American Society of Clinical Oncology website. http://goo.gl/ a0SHt. Published May 20, 2012. Accessed June 7, 2012.
2. Bach PB, Mirkin JN, Oliver TK, et al. Benefits and harms of CT screening for lung cancer: a systematic review [published online ahead of print May 20,2012]. JAMA. doi:10.1001/jama.2012.5521